MeltXone | High Flow Hotend Upgrade

MeltXone | High Flow Hotend Upgrade

Or should we call it the Hyper Spacer? Anyway, you can see it in use in the video below. 

This is a nozzle spacer, like those used to add a CHT nozzle to the volcano hotend, but with some internal geometry to optimize filament melting when combined with a CHT nozzle. In my tests, it resulted in 50% increased warp-free flow. 

Intro

Currently, one of the greatest limitations to high speed printing is the ability to melt plastic fast enough. It might not be the only limitation, but it is a limitation, particularly on larger printers, like my most recent build. 

The CHT nozzle was a tremendous leap for printing speed, letting a standard length hotend match a volcano and a volcano go even further. It splits the flow into 3 paths, increasing surface area, and starts some melting in the center. I'll call the piece in the middle a core splitter for convenience. As the flow increases, solid filament is pressed against the core splitter harder and cools it faster, making it behave less like a hot knife through cold butter and more like a cold knife. Once the heat can't keep up, the filament jams against the solid surface and flow drops. 

The filament needs to be soft enough to split using a mostly blunt surface. If you need further convincing, see Stefan's video, (posted below) comparing the blunt Aliexpress CHT nozzle to the sharp Bondtech one. It might seem sharp, but it's like stabbing a pin through filament. Still too hard for an extruder. 

Even with the core splitter drilled out, the CHT nozzle performs nearly as well as a volcano (see Stefan's graph below). 

Source: 

So if the splitter is the new chokepoint, how do we improve it further? Another video from Stefan shows that splitting the filament earlier has only an effect on extrusion performance, but fails suddenly. In this case, switching between a regular and CHT nozzle made little difference. 

Instead, we can more efficiently heat the filament before it reaches the splitter. A recent study shows that the filament goes unmelted and barely even touches the sides of the meltzone for the first few millimeters (see figures 9 and 10). We can improve the flow rate by optimizing more of the melt zone without jamming the filament straight into the splitter. 

(Figure 9 from Analysis of melting and flow in the hot-end of a material extrusion 3D printer using X-ray computed tomography - ScienceDirect)

3 Solutions

Squished Pipe

The first design is like a pipe squished on one end. As the filament moves forward, it is forced to flatten, increasing the surface area in contact with the meltzone and decreasing the space between the unmelted core and the edges of the meltzone. To prevent flow from being decreased by the hole constricting, the width of the exit is increased enough to have about the same area as the inlet (about 2.5mm^2). This same concept is consistent with the other designs. 

To aid manufacturability, this is designed as 2 mirrored slices of the copper insert that can be pressed into the adapter, like the copper core of the Aliexpress CHT nozzle. This is still likely the most difficult to manufacture, but could be made with a lathe and some determined time with a dremel to carve out the squished-pipe center. 

Triple Cone

The second design is made using a tapered drill bit. One hole is drilled in the center toward the bottom creating the constricting effect that helps melt the filament. On the bottom, three holes are drilled around the first hole, creating a space for melted or softened filament to flow. 

X - The MeltXone

Shown in the video, this is my favorite design. It's got a single tapered hole with notches cut around the perimeter at an angle so they get deeper as the hole gets smaller. It's essentially a more optimized version of the Triple Cone. 

I tested this using a volcano-length meltzone (26.5mm) with Elegoo Hyper PLA at just 215c. My results were just above 45mm^3/s with no warping and 57mm^/s before failure verses 30mm^3/s and 45mm^3/s on the volcano plain spacer+CHT. That's in contrast to the Revo UHF that's extended and was tested at ridiculously high temps (300c) to get their measurements and the Dragon that's extended and has extra length in the heatbreak. 

Room for improvement

• Combine with high flow hotends (Dragon HF)
• Create a nozzle extender (like the one from TriangleLab) using MeltXone geometry
• Simplify manufacturing
• Find cheaper alternatives
• Find a way to manufacture a long version for longer meltzones

Additional resources

Aliexpress nozzle vs Bondtech - sharp tips only have a small effect